Help with 5.0 Stock Hydraulic Lifters

Ok, I've been pounding around forums and google web searches for a few days now and I'm having a hard time finding information on the specifics of what kind of hydraulic lifters came in 5.0's from the factory. I have an '88 with a 5.0 that has a ticking sound after the motor warms up on the passenger side of the engine.

I'm trying to figure out the most cost effective way to fix this ticking because more than anything it's annoying! I'm certain it's not an exhaust leak and when I had the valve cover off I quickly realized the stock rockers aren't adjustable. So from what I've been reading on here and from what people are telling me it must be a worn lifter making the noise. Are stock 5.0 lifters flat or roller? If they are flat can rollers be used as a replacement or will they damage the cam? Does anyone have any suggestions on a good stock replacement part?

I've read a few threads that claim running a thinner oil may help but I'm not too knowledgeable on hydraulic lifters.

Any advice from someone who has replaced lifters or someone who has remedied the same problem I'm having I would be grateful for...

thanks... I changed my oil and filter saturday night. i used conventional 10w30(i usually use 10w40), and my usual FL-A1 filter with a pint of marvel mystery oil.

engine still ticks at low idle, but my newest annoyance is my erratic stock oil gauge. i plan on bypassing it and putting an old Auto Meter sender and gauge in to see how out to lunch i really am, if at all. my oem sender keeps getting too hot from my equal length headers . i'm thinking about plumbing the unit up higher than the header to keep some of the heat off.